X-ray & Optical Images of M31's Core
Twenty-six black hole candidates (labeled in the image) - the largest number found in a galaxy outside our own - have been discovered in the Milky Way's galactic neighbor, Andromeda. Using over 150 Chandra observations spread over 13 years, researchers identified the bonanza of stellar-mass black holes, that is, those that form from the collapse of a giant star and typically have masses between five and ten times that of the Sun. These images show the Chandra view of the central region of Andromeda, also known as M31, with an optical image (red, green, and blue) of the same region. It is expected that billions of years in the future, the Milky Way and Andromeda will collide and many more black holes will be created.
(Credit: X-ray (NASA/CXC/SAO/R.Barnard, Z.Lee et al.), Optical (NOAO/AURA/NSF/REU Prog./B.Schoening, V.Harvey; Descubre Fndn./CAHA/OAUV/DSA/V.Peris)

Optical Image of M31, Wide-field
This wide-field view of Andromeda contains optical data from the Burrell Schmidt telescope of the Warner and Swansey Observatory on Kitt Peak in Arizona. Additional detail of the core and dust in the spiral arms comes from an image taken by astrophotographer Vicent Peris using data from two of his personal telescopes. In this combined optical image, red, green, and blue show different bands from the visible light portion of the electromagnetic spectrum. The marked area shows the region of the Chandra observations (above).
(Credit: NOAO/AURA/NSF/REU Prog./B.Schoening, V.Harvey; Descubre Fndn./CAHA/OAUV/DSA/V.Peris)